As shown in the perspective view of FIG. 1, the prior art document conveying method at the transmitting end is carried out using a device constituted such that an ADF (automatic document feeding) roller 1, a carrying roller 2 and a document detecting device 5 are installed on a document guiding bottom plate 10 having a flat face, the automatically fed document sheets being thus conveyed along the flat face of the bottom plate 10.
To generate gaps between the continuously fed document sheets, the prior art device of FIG. 1 is designed such that the linear speed of the ADF roller 1 should be slower than the linear speed the carrying roller 2. That is, the linear velocity V.sub.A of the ADF roller 1 as against the linear velocity V.sub.F of feeding roller 2 is set to have the following relationship; V.sub.F &gt;V.sub.A.
Therefore, during the time when a document sheet 8 and a document sheet 9 which are continuously fed are being conveyed along the bottom plate 10, if the leading edge and the trailing edge of the two document sheets arrive at the position of the document gap detecting device 5, there is produced a gap between the two document sheets, owing to the difference between the linear velocities of the two document sheets.
Here, the two document sheets are discriminated by the function of the document gap detecting devices 5. That is, in order to discriminate the two document sheets which are continuously fed without gap, the document gap detecting device and the two rollers having different linear velocities are used, while the document gap discriminating device operates only when there is a gap between the two document sheets, the gap being obtained by providing a difference in the linear velocities of the two rollers. According to the standard, the document scanning speed corresponds with the linear velocity of the carrying roller.
However, during the feeding of the document sheet, the document sheet is carried by the ADF roller 1 until the leading edge of the document sheet arrives at the carrying roller.
Meanwhile, although the linear velocity of the ADF roller 1 is designed to be slower than the linear velocity of the carrying roller in order to generate gaps between the document sheets, the scanning speed of the lamp 4 is designed to be same as the linear velocity of the feeding roller 2, and therefore, the scanning speed becomes slower as much as the difference between the linear velocities of the two rollers during the time when the document sheet moves between the scanning starting point and the carrying roller 2. Therefore, of the whole surface of the transmitting document sheet, the portion a which is scanned at a speed the same as the linear velocity of the ADF roller is received to the receiving end with an extended length b as shown in FIG. 1B, and therefore, the received sheet is out off in a changed length c.